1. Technical Field
The present invention relates to an electric gripper system and a control method thereof, and is applicable to an electric gripper for improving the gripper mechanism in terms of positioning accuracy.
2. Description of Related Art
Electric grippers have been extensively used in automated industry for gripping workpieces to be assembled. However, the existing electric gripper tends to have a minor positional deviation from the targeted site every time it moves. Such positional deviation can continuously accumulate. Over time, the electric gripper the difference between the actually reached site and the targeted site can become significant. As a result, the workpiece it holds can leave its intended route and collide with the workpieces on which it is to be assembled.
As disclosed in U.S. Pat. No. 7,863,851, the positional deviation generated when an electric gripper moves is offset. This prior-art device has a first axis for generating a control command that drives a step motor, and a second axis for generating a correct position. Therein, the second axis generates a velocity-curve compensation value according to the position of the motor fed back to it, and then generates a composite command for the step motor by computing the velocity curve compensation value and the control command originally generated by the first axis, thereby compensating the positional deviation of the step motor.
In the prior art as stated above, while it is possible to improve of the accuracy of each-time displacement of the step motor by feeding back the step motor's current position, there is no means to compensate cumulative deviation that results from individual minor positional deviation over several times of the step motor's movement.